This invention relates to a device for mounting components to a structure of the ear for use in a hearing aid system.
In a patient with normally functioning anatomical hearing structures, sound waves are directed into an ear canal by the outer ear and into contact with the tympanic membrane. The tympanic membrane is located at the terminus of the ear canal. The pressure of the sound waves vibrates the tympanic membrane resulting in the conversion to mechanical energy. This mechanical energy is communicated through the middle ear to the inner ear by a series of bones located in the middle ear region. These bones of the middle ear are generally referred to as the ossicular chain, which includes three primary components, the malleus, the incus and the stapes. These three bones must be in functional contact in order for the mechanical energy derived from the vibration of the tympanic membrane to be transferred through the middle ear to the inner ear.
Implantable devices are often useful for assisting with hearing. Such devices include partial middle ear implantable or total middle ear implantable devices, cochlear implants, and other hearing assistance systems that use components disposed in the middle ear or inner ear regions. These components may include an input transducer for receiving sound vibrations or an output stimulator for providing mechanical or electrical output stimuli based on the received sound vibrations. Piezoelectric transducers are one example of a class of electromechanical transducers that require contact to sense or provide mechanical vibrations. For example, the piezoelectric input transducer in U.S. Pat. No. 4,729,366, issued to D. W. Schaefer on Mar. 8, 1998, contacts the malleus for detecting mechanical vibrations. In another example the piezoelectric output transducer in the ""366 patent contacts the stapes bone or the oval or round window of the cochlea.
Devices for assisting the hearing impaired patient range from miniaturized electronic hearing devices which can be adapted to be placed entirely within the auditory canal, or implantable devices which can be completely or partially implanted within the skull. For those hearing systems, or portions of hearing systems, that require complete subcranial implantation, a challenge has existed to adapt the implantable device for optimal mounting to the unique patient morphologies (including both naturally occurring as well as those created by surgical processes) among patients. Known implantable devices that have elements which perform a support or mounting function are typically rigidly mounted to a bone within the middle ear region. Difficulties have arisen with the use of implantable devices in facilitating the fine adjustments necessary to properly position and configure the support assembly and attached transducers so as to contact an auditory element and thus vibrate a portion of the ossicular chain. Such devices present a particular problem in that positioning, or docking, of the transducer against the auditory element in this stable configuration requires extremely fine adjustments that are difficult given the location of the auditory elements and the attendant""s lack of maneuvering room.
A middle ear implantable hearing assistance system typically includes, at least, an input device, such as a sensor transducer, an output device, such as a driver transducer, and some means for electrically connecting the devices and coupling at least one device to an element of the middle ear. The transducer is coupled to and communicates with the middle ear element via a mechanical coupling. The mechanical coupling is critical to the efficacy of the hearing assistance system. Proper positioning of the transducer and good contact between the transducer and ossicle is essential to properly transducing the received mechanical vibrations into a resulting electrical signal for hearing assistance processing (in the case of a sensor transducer) or communicating to the ossicle the mechanical vibration transduced from the electrical signal (in the case of a driver transducer).
It is unclear whether too much force between the transducer and the ossicle, for example the malleus, can mechanically load the vibrating malleus and attenuate the desire mechanical vibration signal or alter its frequency characteristics. It may be likely that, in an extreme case, too much force can damage or break either the malleus or the transducer. It may also be likely that too little force between the transducer and the malleus may be insufficient to detect the mechanical vibration signal, and is more likely to result in a complete loss of signal detection if the transducer and the malleus become dissociated.
Positive fixation is when a device accommodates the morphology of the ossicle or tissue which it is connecting (directly or indirectly). Many prior art devices do not account for the morphological differences of each patient. Such prior art devices either harm the patient by not taking into account, fully, the detrimental impact on tissue patency caused by its structural method of attachment, are nonfunctional, or lose functioning ability with drops of pressure. Specifically, when a transducer is too loosely coupled to the ossicle, there is no signal and, conversely, when a transducer is too tightly coupled to the ossicle, there may be a less than optimum frequency response or harm to the tissue.
Prior art coupling mechanisms used, for example, in coupling a transducer to an ossicle, have a variety of problems. Biasing or crimping have commonly been used to attach to an ossicle. Biasing may result in a connection which is too loose because of the difficulty in determining the extent of the biasing. Over a patient""s lifespan, muscles, tissue, and ligaments may stretch and cause the biasing to become loose. Additionally, even if the biased element is not loose during everyday activity, it may become loose and lose contact altogether with a change in pressure, such as in an elevator or an airplane. Crimping has similar problems. It is difficult to determine when the element has been adequately crimped to the ossicle. If the element is too tightly crimped to the ossicle, the blood vessels lose patency and bone rotting to occur. If the element is too loosely crimped to the ossicle, there may be resonances and a poor frequency response.
Similar problems occur when coupling an ossicle to a passive prosthesis. A passive prosthesis is used when one or more of the malleus, incus, or stapes is partially or completely removed or damaged. The passive prosthesis maintains functional contact to transfer the mechanical energy derived from the vibration of the tympanic membrane through the middle ear to the inner ear.
While using an adhesive results in positive coupling with an ossicle, the procedures for securing the transducer or prosthesis to the ossicle are frequently time consuming and technically challenging. In the case of a transducer, the transducer must be positioned with mechanical contact to the ossicle. In positioning the transducer, a physician frequently grasps the transducer with forceps and uses the forceps to maneuver the transducer. The forceps and transducer is often large and unwieldy in the relatively small middle-ear space.
After positioning, the adhesive must be applied to the contact region of the transducer to the ossicle. Adhesives have a setting or curing time during which the transducer must remain in substantially the same position. Thus, the transducer must be remain substantially stable for, generally, at least 15 minutes. This can pose a challenge to a physician who is manually holding the transducer in place with forceps.
Similarly, it is in technically challenging to place and adhere a bracket to the mastoid floor. Typically, a bracket is used to hold a transducer in contact with a transducer and is mounted on and adhered to the mastoid floor. A common method for adhering the brackets is to use an adhesive wherein the adhesive is injected into the area and the bracket is then held in the adhesive with forceps. This method requires the bracket to be held in substantially the same position until the cement sets.
The support device of the present invention is of particular use in the positioning and supporting of devices to be in contact with a structure of the ear.
To address the difficulties noted above, the present invention provides a device for more effectively and accurately positioning and supporting an element for contact with a structure of the ear. While reference is made explicitly to mounting a transducer to an ossicle, it should be apparent to those skilled in the art that the device could be used for coupling any desired device to an auditory element of the ear.
A flexible support for aid in positioning elements in contact with an auditory element is described. The present invention utilizes a flexible device to support and position a transducer against the ossicle. The device may be used equally well in positioning a passive prosthesis or similar device.
The device involves a flexible element having two ends. The first end is detachably affixed to the transducer (or other element to be positioned). The second end is configured as a mount attachable to a base, for example along the mastoid cavity. In positioning the transducer, the mount is attached to the base via a fastener, for example a screw. The flexible element may then be manipulated to position the transducer as desired. Once in position, the flexible element is rigid enough to support the transducer in position without further instrumentation. Thus, adhesive can be applied and the flexible element will maintain position of the transducer as the adhesive cures. After positioning and adhering of the transducer, the flexible element is disconnected from the transducer and removed from the base.